The present invention relates to an apparatus for positioning out-of-round workpieces, particularly piston rings, which have an out-of-round inner circumferential face with a radially inwardly directed portion that deviates from the normal out-of-round contour.
Piston ring blanks are provided with centering devices which permit alignment of a plurality of blanks in the circumferential direction so that they may be machined together. For example, according to the book "Kolbenringe" [Piston Rings] by Carl Englisch, published by Springer Verlag, Vienna, 1958, page 285, FIG. 266, piston ring blanks provided for this purpose each have a centering notch at their inner circumference. The notches lie in the area of the abutment opening of the finished piston rings and are later removed during the machining operation. A shaft having a diameter of approximately 4 mm is rotated at a speed of about 120 revolutions per minute in contact with the rings thereby causing them to rotate, the notches holding the rings on the shaft. Using this sorting technique, a relatively long time is required to align all of the blanks.
Further, during the sorting procedure, individual rings are sometimes caught by adjacent, already stopped, rings and therefore all of the rings may not attain their final position making optical surveillance on the part of the machine operator necessary. Moreover, the notch in the ring blank has an adverse effect on the machining process, the brief, abrupt interruption of the machining process leading to resonant oscillations which produce chatter marks on the rings and considerably reduce the service life of the tool. In addition, the notch limits the cutting speed and therefore the maximum output of the machine.
German Pat. No. 745,686 discloses an arrangement for simultaneously measuring the diameter of a shaft at several points. In this apparatus, the shaft is disposed in a rigid straddle support and is scanned at various locations by a measuring sensor disposed in the angle bisector of the support to detect deviations in the shaft diameter. For this purpose, the shaft is manually rotated in the support in the circumferential direction.
Still another publication, VDI Report No. 230, for the year 1975, page 70, FIG. 16 discloses a measuring device for checking the outer diameter, conicity and linearity of the superficies and out-of-roundness of piston bolts. In this device, piston bolts are introduced automatically and then pressed by means of a pressing device against two rollers which rotate in the same direction. The individual measurements are made during several revolutions of the piston bolts following which the piston bolts are ejected.
The above-described devices are employed exclusively for measuring purposes and cannot be used, in their present form, to position out-of-round workpieces.
It is an object of the present invention to provide an improved apparatus for positioning an out-of-round workpiece wherein the above-described disadvantages are avoided.
It is another object of the invention to provide an improved apparatus wherein out-of-round workpieces without notches can be positioned at their inner circumferences.